期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 480, 期 2, 页码 1499-1506出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnras/sty1808
关键词
instabilities; solar wind; plasmas
资金
- National Science Foundation [NSF PHY-1707272]
- National Aeronautics and Space Administration [NASA 80NSSC18K0646]
- Vilas Associates Award from the University of Wisconsin - Madison
In this work, we analyse the kinetic stability of a solar wind electron distribution composed of core and strahl subpopulations. The core is modelled by a drifting Maxwellian distribution, while the strahl is modelled by an analytic function recently derived in (Horaites et al. 2018) from the collisional kinetic equation. We perform a numerical linear stability analysis using the LEOPARD solver (Astfalk & Jenko 2017), which allows for arbitrary gyrotropic distribution functions in a magnetized plasma. In contrast with previous reports, we do not find evidence for a whistler instability directly associated with the electron strahl. This may be related to the more realistic shape of the electron strahl distribution function adopted in our work, as compared to previous studies. We, however, find that for typical solar wind conditions, the core-strahl distribution is unstable to the kinetic Alfven and magnetosonic modes. The maximum growth rates for these instabilities occur at wavenumbers kd(i) less than or similar to 1 (where d, is the ion inertial length), at moderately oblique angles of propagation, thus providing a potential source of kinetic-scale turbulence. We therefore suggest that if the whistler modes are invoked to explain anomalous scattering of strahl particles, these modes may appear as a result of nonlinear mode coupling and turbulent cascade originating at scales kd(i) less than or similar to 1.
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